In order to drive a machine tool by means of a numerical control apparatus, it is necessary to transfer signals between the numerical control apparatus and the machine side. This signal transfer is carried out by means of wires, such as cables, that are connected between the numerical control apparatus and input/output terminals on the machine side. In general, the connection between the numerical control apparatus and the machine side varies depending on various conditions, such as the type and scale of a machine in a system of the machine side. Conventionally, therefore, a distribution board and an I/O unit are employed for facilitating the connections with cables and the like to the machine-side system. In such a case, the distribution board is manufactured for each machine so that it can fit the machine to be controlled by means of the numerical control apparatus, while, for the I/O unit, commonly available is used.
FIG. 3 is a block diagram for illustrating the connection between a conventional numerical control apparatus and a machine side. Referring to FIG. 3, an I/O unit 24 and a distribution board 23 are arranged between a numerical control apparatus 21 and a machine side 22, and are connected by means of cables 31, 32, 33 and 34. The distribution board 23 is set corresponding to the machine-side system 22.
The I/O connection between the conventional numerical control apparatus and the machine side has problems in terms of operating efficiency and productivity.
In making the I/O connection between the conventional numerical control apparatus and the machine side, the distribution board 23 is set singly corresponding to the system of the machine side 22, as shown in FIG. 3, for example. Moreover, on the machine side of the I/O unit 24, the I/O unit 24 and the machine side 22 require at least two cables (wires 32 and wires 33 and 34) between themselves and the distribution board 23. Accordingly, the distribution board 23 must be set corresponding to the machine-side system, and the number of cables for the connection to the distribution board 23 has to be increased, so that it is difficult to improve the operating efficiency and productivity of the distribution board.
In the case where the volume of signals between the numerical control apparatus 21 and the machine side 22 is increased, as shown in FIG. 4, it becomes necessary to use two distribution boards (23a and 23b) and additional I/O units 24a and 24b corresponding to the distribution boards 23a and 23b. These distribution boards and I/O units must be manufactured independently corresponding to the arrangement of the machine side 22, and the number of cables for the connection between them increases accordingly.
By manufacturing the I/O units of the numerical control apparatus adapting to the machine side 22, the distribution boards themselves may be omitted to prevent the increase in the number of cables attributable to the increase of the distribution boards. In this case, however, an I/O unit must be manufactured for each of different machine tools. In general, however, an I/O unit requires a communication circuit, which transmits and receives signals to and from the body of the numerical control apparatus itself, and a transmitter-receiver circuit, which transmits and receives signals to and from the machine side. Thus, providing these circuits for each of different machine tools entails high manufacturing and operating costs.